Method for preparing soybean protein isolate gel from organic acid compound TG enzyme

Abstract

The invention discloses a method for preparing soybean protein isolate gel from an organic acid compound TG enzyme, which comprises the following steps: preparing a 12% soybean protein isolate solution, adding 40 U / g TG enzyme, adding an organic acid compound, and stirring to obtain a mixed solution, the organic acid compound being any one of gluconic acid-delta-lactone, lactobionic acid and maltose acid; carrying out water bath at 40 DEG C for 1 hour, transferring to water bath at 95 DEG C, and heating for 30 minutes; taking out after heating, and cooling in an ice-water bath for 10 minutes; and storing overnight at 4 DEG C to obtain the soybean protein isolate gel. According to the invention, the problems of insufficient gel strength of soybean protein in the application process, limited water binding capacity and the like can be solved, and the texture property of the soybean protein isolate gel is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of food processing, in particular to the technical field of plant protein gel preparation, and specifically to a method for preparing soy protein isolate gel by using an organic acid compound TG enzyme. Background Art

[0002] In the food industry, soy protein isolate has become an important plant protein resource due to its rich nutritional content and diverse functional properties. Furthermore, as a sustainable plant protein source, soy protein isolate can effectively replace animal protein, reduce the intake of cholesterol and saturated fatty acids, and has a relatively low impact on the environment, thus meeting the requirements of sustainable development. These advantages enable soy protein isolate to not only meet the food industry's demand for high-quality protein, but also provide important support for promoting the development of healthy foods and the construction of a sustainable food system. However, traditional soy protein isolate gels still have shortcomings in terms of texture, elasticity, and water retention, which limits their application in food processing.

[0003] Transglutaminase (TG enzyme) is an enzyme that can catalyze acyl transfer reactions. It can efficiently catalyze acyl transfer reactions, a process that is crucial for the cross-linking and modification of proteins. During the catalytic process, TG enzyme uses the γ-carboxamide group of glutamine residues in proteins and peptide bonds as an acyl donor, and reacts with acyl acceptors to form covalent bonds, thereby achieving cross-linking between protein molecules or the binding of proteins to other molecules. TG enzyme cross-linking can significantly enhance the hardness, elasticity and water retention of soy protein isolate gels. Although TG enzyme can form a gel network structure during the cross-linking process, the structure still needs to be further optimized in terms of uniformity and stability.

[0004] However, the existing TG enzyme cross-linking technology still has significant shortcomings:

[0005] 1. Insufficient gel strength: The gel strength of soy protein treated with pure TG enzyme is only 60%-70% of that of animal protein gel, which is difficult to meet the needs of high-end products;

[0006] 2. Limited water holding capacity: Under the existing process, the water holding capacity is improved by less than 15%, and the water loss rate during high-temperature storage is as high as 20%;

[0007] 3. Complex process: To maintain the activity of TG enzyme, the pH value (6.5-7.5) and temperature (40-50°C) need to be strictly controlled, which increases the equipment and energy consumption costs.

[0008] Recent studies have attempted to improve performance by adding excipients (such as polysaccharides and phosphates) or using complex enzymes, but this can introduce unpleasant odors or increase the risk of allergies. Therefore, developing a method that can synergistically improve the overall performance of gels without requiring complex additives is of great significance for promoting the industrialization of plant protein foods. Summary of the Invention

[0009] In order to overcome the shortcomings of the existing technology, the purpose of the present invention is to provide a method for preparing soy protein isolate gel by combining organic acid with TG enzyme, so as to solve the problems of insufficient gel strength of soy protein during application and limited water holding capacity, and improve the texture properties of soy protein isolate gel.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A method for preparing soy protein isolate gel by using an organic acid compound TG enzyme comprises the following steps:

[0012] Step 1, preparing a soy protein isolate solution with a mass volume ratio of 12% (w / v, 12g soy protein isolate / 100mL water), and stirring at room temperature; the room temperature is 18-30°C;

[0013] Step 2, adding 40 U / g TG enzyme (40 U TG enzyme / g protein) to the protein solution to mix the TG enzyme with the protein solution;

[0014] Step 3, adding an organic acid to the protein solution to which TG enzyme has been added and stirring to obtain a mixed solution, wherein the organic acid is any one of glucono-δ-lactone, lactobionic acid, and maltobionic acid; when the organic acid is glucono-δ-lactone, the mass volume ratio of glucono-δ-lactone to the protein solution is 0.4% to 1.0% (w / v, g / 100 mL); when the organic acid is lactobionic acid, the mass volume ratio of lactobionic acid to the protein solution is 0.8%; when the organic acid is maltobionic acid, the mass volume ratio of maltobionic acid to the protein solution is 0.8% to 1.0%;

[0015] Step 4: Place the mixed solution into a container and seal it to prevent water evaporation and contamination by external impurities; place it in a 40°C water bath for 1 hour; and keep the water bath temperature stable during this process;

[0016] Step 5: The mixture was transferred to a water bath and heated at 95°C for 30 minutes to further promote gel formation and cross-linking reaction.

[0017] Step 6: After heating, take out the gel and cool it in an ice water bath for 10 minutes to allow the gel to cool down quickly and set;

[0018] Step 7: Storing the mixture at 4° C. overnight to further stabilize and optimize the gel structure, thereby obtaining the soy protein isolate gel.

[0019] For further optimization, the soy protein isolate solution in step 1 was stirred at 500 rpm for 2 h at room temperature to fully dissolve the soy protein isolate and form a uniform solution.

[0020] Furthermore, after adding the TG enzyme in step 2, the mixture was stirred for 30 minutes to uniformly disperse the TG enzyme in the solution system.

[0021] Furthermore, in step 4, during the reaction in a 40° C. water bath for 1 h, the solution was stirred at a speed of 500 rpm.

[0022] Furthermore, in step 5, during the heating in a 95° C. water bath for 30 min, the power of the heating device is 800 W.

[0023] Furthermore, during the ice-water bath cooling in step 6, the mass ratio of ice to water is 1:2.

[0024] The beneficial effects of the present invention compared to the prior art are:

[0025] 1) Enhanced gel strength: By adding specific organic acids, the gel's hardness, elasticity and other strength indicators are significantly improved. For example, when glucono-δ-lactone is added at a concentration of 1% (w / v), the gel's hardness increases by 11.49N, its elasticity increases by 9.63mm, and its gel strength reaches 4.50g / cm 2 , which can better meet the requirements for gel strength in food processing and material applications.

[0026] 2) Enhanced water retention: For example, when lactobionic acid was added at a concentration of 0.8% (w / v), the water retention of the gel increased to 99.77%. When maltodextrin was added at a concentration of 1% (w / v), the water retention of the gel increased to 99.91%. When glucono-δ-lactone was added at a concentration of 1%, the water retention of the gel increased to 100%. This result shows that the addition of organic acidic substances in the present invention can effectively improve the water retention performance of the gel, reducing water loss during storage and use. This improvement in water retention not only extends the shelf life of the product, but also improves the taste and quality of the gel.

[0027] 3) The method of the present invention is suitable for the industrial production of plant-based meat products, cheese substitutes, etc., and has significant market application value BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings and examples.

[0029] Figure 1 A: Microstructure of soy protein isolate gel prepared by composite TG enzyme without adding organic acid (Comparative Example 1);

[0030] Figure 1 B: Microstructure of the soy protein isolate gel prepared by composite TG enzyme at the optimal addition concentration of glucono-δ-lactone (Example 4).

[0031] Figure 1 C: Microstructure of soy protein isolate gel prepared by composite TG enzyme at the optimal addition concentration of maltobionate (Example 6).

[0032] Figure 1 D: Microstructure of soy protein isolate gel prepared by composite TG enzyme at the optimal addition concentration of lactobionic acid (Example 7).

[0033] Figure 1 A- Figure 1 The acceleration voltage of the D electron beam was 5.00 kV and the magnification was 500 times, showing the effect of different organic acid addition concentrations on the microstructure of soy protein isolate gel.

[0034] Figure 2 A: Relaxation curve analysis of a soy protein isolate gel prepared with a complex TG enzyme at optimal concentrations of glucono-δ-lactone, maltobionic acid, and lactobionic acid. Measurements were made using a low-frequency nuclear magnetic resonance (NMR) analyzer and a CPMG pulse sequence. The relaxation time ranged from 0.01 ms to 10,000 ms.

[0035] Figure 2 B: Analysis of the moisture distribution of soy protein isolate gel prepared by composite TG enzyme at the optimal addition concentration of glucono-δ-lactone, maltobionic acid and lactobionic acid.

[0036] Figure 3 A: Zeta potential of soy protein isolate gel prepared by composite TG enzyme at the optimal addition concentration of glucono-δ-lactone, maltobionic acid and lactobionic acid.

[0037] Figure 3 B: The particle size of soy protein isolate gel prepared by composite TG enzyme at the optimal addition concentration of glucono-δ-lactone, maltobionic acid and lactobionic acid.

[0038] Figure 3 C: Surface hydrophobicity analysis of soy protein isolate gel prepared by composite TG enzyme at the optimal addition concentration of glucono-δ-lactone, maltobionic acid and lactobionic acid.

[0039] Figure 4: Rheological properties of soy protein isolate gel prepared by composite TG enzyme at the optimal addition concentration of glucono-δ-lactone, maltobionic acid and lactobionic acid. Figure 4 A is G', Figure 4 B is G". DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0041] Example 1

[0042] This embodiment provides a method for preparing a soy protein isolate gel using an organic acid compound TG enzyme, comprising the following steps:

[0043] Step 1: dissolving soy protein isolate in water to form a solution with a mass volume ratio of 12% (w / v), and stirring at 500 rpm for 2 hours at room temperature; the room temperature is 18-30° C.;

[0044] Step 2: Add 40 U / g TG enzyme to the above solution and stir for 30 minutes to fully mix the TG enzyme and protein solution;

[0045] Step 3, adding glucono-δ-lactone to the protein solution to a concentration of 0.4% (w / v), and stirring thoroughly to obtain a mixed solution;

[0046] Step 4: The resulting mixture was divided into 50 mL beakers, sealed with plastic wrap, and placed in a 40°C water bath for reaction for 1 h; the solution was stirred at a stirring speed of 500 rpm;

[0047] Step 5: Transfer the beaker to a 95°C water bath and heat for 30 minutes at a power of 800W.

[0048] Step 6: Remove the beaker and place it in an ice-water bath to cool for 15 minutes. The mass ratio of ice to water is 1:2.

[0049] Step 7, the mixture is then stored at 4° C. overnight to obtain a glucono-δ-lactone-TG enzyme cross-linked soy protein isolate gel.

[0050] The gel prepared in this example was tested for performance, and the gel strength was 3.25 g / cm 2 , water holding capacity is 99.55%, hardness is 7.62N, and elasticity is 10.48mm.

[0051] Example 2

[0052] This example provides a method for preparing soy protein isolate gel using an organic acid compound TG enzyme. The raw materials used are the same as those in Example 1. The difference between the preparation method and Example 1 is that:

[0053] In step 3, glucono-δ-lactone is added to the protein solution to a concentration of 0.6% (w / v), and the solution is stirred thoroughly.

[0054] The gel prepared in this example was tested for performance, and the gel strength was 3.94 g / cm 2 , water holding capacity is 99.94%, hardness is 12.85N, and elasticity is 10.59mm.

[0055] Example 3

[0056] This example provides a method for preparing soy protein isolate gel using an organic acid compound TG enzyme. The raw materials used are the same as those in Example 1. The difference between the preparation method and Example 1 is that:

[0057] In step 3, glucono-δ-lactone is added to the protein solution to a concentration of 0.8% (w / v), and the mixture is stirred thoroughly.

[0058] The gel prepared in this example was tested for performance, and the gel strength was 3.70 g / cm 2 , water holding capacity is 100.00%, hardness is 14.42N, and elasticity is 12.06mm.

[0059] Example 4

[0060] This example provides a method for preparing soy protein isolate gel using an organic acid compound TG enzyme. The raw materials used are the same as those in Example 1. The preparation method differs from that in Example 1 in that:

[0061] In step 3, glucono-δ-lactone is added to the protein solution to a concentration of 1.0% (w / v), and the mixture is stirred thoroughly.

[0062] The gel prepared in this example was tested for performance, and the gel strength was 4.50 g / cm 2 , water holding capacity is 100.00%, hardness is 15.66N, and elasticity is 12.58mm.

[0063] Example 5

[0064] This example provides a method for preparing soy protein isolate gel using an organic acid compound TG enzyme. The preparation method thereof differs from that of Example 1 in that:

[0065] In step 3, maltobionate is added to the protein solution to a concentration of 0.8% (w / v), and the mixture is stirred thoroughly.

[0066] The gel prepared in this example was tested for performance, and the gel strength was 1.79 g / cm 2 , water holding capacity is 99.60%, hardness is 4.99N, and elasticity is 10.95mm.

[0067] Example 6

[0068] This example provides a method for preparing soy protein isolate gel using an organic acid compound TG enzyme. The preparation method thereof differs from that of Example 1 in that:

[0069] In step 3, maltobionate is added to the protein solution to a concentration of 1.0% (w / v), and the mixture is stirred thoroughly.

[0070] The gel prepared in this example was tested for performance, and the gel strength was 2.16 g / cm 2 , water holding capacity is 99.91%, hardness is 5.97N, and elasticity is 14.73mm.

[0071] Example 7

[0072] This example provides a method for preparing soy protein isolate gel using an organic acid compound TG enzyme. The preparation method thereof differs from that of Example 1 in that:

[0073] In step 3, lactobionic acid is added to the protein solution to a concentration of 0.8% (w / v), and the mixture is stirred thoroughly.

[0074] The gel prepared in this example was tested for performance, and the gel strength was 2.76 g / cm 2 , water holding capacity is 99.77%, hardness is 10.12N, and elasticity is 10.12mm.

[0075] Comparative Example 1

[0076] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0077] In step 3, no organic acid is added to the protein solution.

[0078] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.56 g / cm 2 , water holding capacity is 89.61%, hardness is 4.17N, and elasticity is 2.95mm.

[0079] Comparative Example 2

[0080] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0081] In step 3, citric acid is added to the protein solution to a concentration of 0.2% (w / v), and the mixture is stirred thoroughly.

[0082] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.38 g / cm 2 , water holding capacity is 99.62%, hardness is 3.24N, and elasticity is 4.15mm.

[0083] Comparative Example 3

[0084] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0085] In step 3, citric acid is added to the protein solution to a concentration of 0.4% (w / v), and the mixture is stirred thoroughly.

[0086] The gel prepared in this comparative example was subjected to performance testing, and the gel strength was 1.28 g / cm 2 , water holding capacity is 93.35%, hardness is 3.01N, and elasticity is 3.73mm.

[0087] Comparative Example 4

[0088] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0089] In step 3, citric acid is added to the protein solution to a concentration of 0.6% (w / v), and the mixture is stirred thoroughly.

[0090] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.06 g / cm 2 , water holding capacity is 94.66%, hardness is 2.52N, and elasticity is 4.58mm.

[0091] Comparative Example 5

[0092] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0093] In step 3, citric acid is added to the protein solution to a concentration of 0.8% (w / v), and the mixture is stirred thoroughly.

[0094] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.18 g / cm 2 , water holding capacity is 89.41%, hardness is 2.86N, and elasticity is 4.34mm.

[0095] Comparative Example 6

[0096] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0097] In step 3, citric acid is added to the protein solution to a concentration of 1.0% (w / v), and the mixture is stirred thoroughly.

[0098] The performance test of the gel prepared in this comparative example showed that the gel strength was 0.56 g / cm 2 , water holding capacity is 83.11%, hardness is 2.65N, and elasticity is 3.98mm.

[0099] Comparative Example 7

[0100] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0101] In step 3, malic acid is added to the protein solution to a concentration of 0.2% (w / v), and the mixture is stirred thoroughly.

[0102] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.30 g / cm 2 , water holding capacity is 99.70%, hardness is 4.25N, and elasticity is 7.97mm.

[0103] Comparative Example 8

[0104] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0105] In step 3, malic acid is added to the protein solution to a concentration of 0.4% (w / v), and the mixture is stirred thoroughly.

[0106] The performance test of the gel prepared in this comparative example showed that the gel strength was 0.43 g / cm 2 , water holding capacity is 94.74%, hardness is 3.27N, and elasticity is 3.98mm.

[0107] Comparative Example 9

[0108] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0109] In step 3, malic acid is added to the protein solution to a concentration of 0.6% (w / v), and the mixture is stirred thoroughly.

[0110] The performance test of the gel prepared in this comparative example showed that the gel strength was 0.24 g / cm 2 , water holding capacity is 89.84%, hardness is 3.21N, and elasticity is 3.96mm.

[0111] Comparative Example 10

[0112] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0113] In step 3, malic acid is added to the protein solution to a concentration of 0.8% (w / v), and the mixture is stirred thoroughly.

[0114] The performance test of the gel prepared in this comparative example showed that the gel strength was 0.21 g / cm 2 , water holding capacity is 91.35%, hardness is 1.72N, and elasticity is 4.56mm.

[0115] Comparative Example 11

[0116] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0117] In step 3, malic acid is added to the protein solution to a concentration of 1.0% (w / v), and the mixture is stirred thoroughly.

[0118] The performance test of the gel prepared in this comparative example showed that the gel strength was 0.34 g / cm 2 , water holding capacity is 85.88%, hardness is 1.70N, and elasticity is 6.01mm.

[0119] Comparative Example 12

[0120] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0121] In step 3, succinic acid is added to the protein solution to a concentration of 0.2% (w / v), and the mixture is stirred thoroughly.

[0122] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.29 g / cm 2 , water holding capacity is 99.60%, hardness is 4.14N, and elasticity is 9.62mm.

[0123] Comparative Example 13

[0124] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0125] In step 3, succinic acid is added to the protein solution to a concentration of 0.4% (w / v), and the mixture is stirred thoroughly.

[0126] The performance test of the gel prepared in this comparative example showed that the gel strength was 0.78 g / cm 2 , water holding capacity is 91.06%, hardness is 2.02N, and elasticity is 3.76mm.

[0127] Comparative Example 14

[0128] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0129] In step 3, succinic acid is added to the protein solution to a concentration of 0.6% (w / v), and the mixture is stirred thoroughly.

[0130] The performance test of the gel prepared in this comparative example showed that the gel strength was 0.19 g / cm 2 , water holding capacity is 78.59%, hardness is 1.27N, and elasticity is 3.04mm.

[0131] Comparative Example 15

[0132] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0133] In step 3, succinic acid is added to the protein solution to a concentration of 0.8% (w / v), and the mixture is stirred thoroughly.

[0134] The performance test of the gel prepared in this comparative example showed that the gel strength was 0.54 g / cm 2 , water holding capacity is 84.62%, hardness is 1.47N, and elasticity is 4.70mm.

[0135] Comparative Example 16

[0136] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0137] In step 3, succinic acid is added to the protein solution to a concentration of 1.0% (w / v), and the mixture is stirred thoroughly.

[0138] The performance test of the gel prepared in this comparative example showed that the gel strength was 0.43 g / cm 2 , water holding capacity is 85.53%, hardness is 1.25N, and elasticity is 2.76mm.

[0139] Comparative Example 17

[0140] This comparative example provides a method for preparing soy protein isolate gel. The raw materials used are the same as those in Example 1. The difference between the preparation method and Example 1 is that:

[0141] In step 3, glucono-δ-lactone is added to the protein solution to a concentration of 0.2% (w / v), and the solution is stirred thoroughly.

[0142] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.23 g / cm 2, water holding capacity is 99.16%, hardness is 3.90N, and elasticity is 8.97mm.

[0143] Comparative Example 18

[0144] This embodiment provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0145] In step 3, maltobionate is added to the protein solution to a concentration of 0.2% (w / v), and the mixture is stirred thoroughly.

[0146] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.37 g / cm 2 , water holding capacity is 99.24%, hardness is 3.44N, and elasticity is 9.51mm.

[0147] Comparative Example 19

[0148] This comparative example provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0149] In step 3, maltobionate is added to the protein solution to a concentration of 0.4% (w / v), and the mixture is stirred thoroughly.

[0150] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.36 g / cm 2 , water holding capacity is 99.32%, hardness is 3.77N, and elasticity is 10.20mm.

[0151] Comparative Example 20

[0152] This embodiment provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0153] In step 3, maltobionate is added to the protein solution to a concentration of 0.6% (w / v), and the mixture is stirred thoroughly.

[0154] The gel prepared in this example was tested for performance, and the gel strength was 1.33 g / cm 2 , water holding capacity is 99.71%, hardness is 4.41N, and elasticity is 10.43mm.

[0155] Comparative Example 21

[0156] This embodiment provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0157] In step 3, lactobionic acid is added to the protein solution to a concentration of 0.2% (w / v), and the mixture is stirred thoroughly.

[0158] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.55 g / cm 2 , water holding capacity is 99.78%, hardness is 3.68N, and elasticity is 6.57mm.

[0159] Comparative Example 22

[0160] This embodiment provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0161] In step 3, lactobionic acid is added to the protein solution to a concentration of 0.4% (w / v), and the mixture is stirred thoroughly.

[0162] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.68 g / cm 2 , water holding capacity is 99.68%, hardness is 3.81N, and elasticity is 8.17mm.

[0163] Comparative Example 23

[0164] This embodiment provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0165] In step 3, lactobionic acid is added to the protein solution to a concentration of 0.6% (w / v), and the mixture is stirred thoroughly.

[0166] The performance test of the gel prepared in this comparative example showed that the gel strength was 1.66 g / cm 2 , water holding capacity is 99.68%, hardness is 5.81N, and elasticity is 9.50mm.

[0167] Comparative Example 24

[0168] This embodiment provides a method for preparing a soy protein isolate gel, which differs from that of Example 1 in that:

[0169] In step 3, lactobionic acid is added to the protein solution to a concentration of 1.0% (w / v), and the mixture is stirred thoroughly.

[0170] The gel prepared in this comparative example was subjected to performance testing, and the gel strength was 2.13 g / cm 2 , water holding capacity is 99.73%, hardness is 9.25N, and elasticity is 10.57mm.

[0171] Table 1 Effects of different organic acids added on the gel strength of TG enzyme cross-linked soy protein isolate gel

[0172]

[0173]

[0174]

[0175] Note: Different lowercase letters indicate significant differences within the groups with different concentrations of organic acid (P<0.05) Table 2 Effects of different organic acids on the water holding capacity of TG enzyme cross-linked soy protein isolate gel

[0176]

[0177]

[0178] Note: Different lowercase letters indicate significant differences within the groups with different concentrations of organic acid (P<0.05) Table 3 Effects of different organic acids on the texture parameters of TG enzyme cross-linked soy protein isolate gel

[0179]

[0180]

[0181] Note: Different lowercase letters indicate significant differences within the groups with different organic acid concentrations (P<0.05) Table 4 Analysis of molecular interactions of soy protein isolate gel prepared by composite TG enzyme at the optimal addition concentrations of glucono-δ-lactone, lactobionic acid and maltobionic acid

[0182]

[0183]

[0184] Note: Different lowercase letters indicate significant differences among the groups with different organic acid additions (P<0.05).

[0185] Results and analysis of the examples and comparative examples:

[0186] From Table 1 and Figure 1 It can be seen that the comparative example 1 (without organic acid): gel strength is 1.56 g / cm 2 , hardness 4.17N, elasticity 2.95mm, loose network (SEM shows pore size> 200μm), relying only on the basic cross-linking effect of TG enzyme. Example 4 Gel strength reaches 4.50g / cm 2(+188%), hardness 15.66N (+276%), elasticity 12.58mm (+326%), SEM shows a continuous dense three-dimensional network (pore size <50μm), attributed to the sustained release acidification of glucono-δ-lactone to promote protein unfolding, exposing more TG enzyme cross-linking sites, and can effectively enhance the structural stability of TG enzyme cross-linked soy protein isolate gel and promote the formation of gel network. This shows that Example 4 has higher cross-linking efficiency and stronger network formation ability in the gel system. This high-strength gel structure can not only better retain moisture, but also maintain a stable morphology under external pressure and has good mechanical properties. Example 6 Gel strength 2.16g / cm 2 (+38%), hardness 5.97N (+43%), elasticity 14.73mm (+399%), the structure shows a medium density of pores (pore diameter ~100μm), the hydroxyl groups of maltobionic acid are cross-linked through hydrogen bonds, the surface pores are reduced, and the structure becomes more dense. Example 7 Gel strength 2.76g / cm 2 (+77%), hardness 10.12N (+143%), elasticity 10.12mm (+243%), there are local aggregation areas in the network structure, the carboxylic acid groups of lactobionic acid chelate with calcium ions to enhance local cross-linking, the surface pores are reduced, and the structure becomes denser, but the gel surface is still relatively rough, lacking flatness and uniformity.

[0187] From Table 2 and Figure 2 B shows that the water retention rate of comparative example 1 is 89.61%, with free water accounting for 4%. The water retention rate of example 4 is as high as 100%, with free water accounting for only 10% and bound water accounting for 90%. Glucono-δ-lactone induces the transformation of β-sheet → random coil through sustained release acidification, forming nanopores (average particle size 170nm, Figure 3 B), synergistically locks water through capillary action and hydrophobic interaction (hydrophobic force 7.67 in Table 4). Example 6 has a water retention rate of 99.91% and free water of 6%. The polyhydroxy structure of maltobionic acid enhances the hydrogen bond network (Table 4: hydrogen bond-hydrophobic force 2.17), but the pore size is small (average particle size 157nm, Figure 3 B) results in free water remaining. Example 7: water retention is 99.77%, free water is 6%, lactobionic acid chelation stabilizes calcium bridge (Zeta potential -6.81mV, Figure 3 A), but local charge unevenness causes fluctuations in water distribution.

[0188] Depend on Figure 4It can be obtained that the rheological properties of the TG enzyme cross-linked soy protein isolate gels prepared in Example 4, Example 6 and Example 7 were analyzed. The results showed that within the entire frequency variation range, the storage modulus (elastic modulus) G' of all gel samples was greater than the loss modulus (viscous modulus) G", indicating that these gels had strong elastic characteristics, exhibited gel-like behavior, and all gels exhibited a solid-like state. In addition, the G' and G" of the prepared gels increased with increasing frequency, showing a strong frequency dependence, which indicates that the gel system prepared in this experiment belongs to a "weak gel" system. The G' and G" values of the gel in Example 4 reached the highest, indicating that it significantly enhanced the cross-linking density between protein molecules through charge neutralization effect and ion bridging, forming a more rigid three-dimensional network structure.

[0189] Example 4: Through the three-stage cascade reaction of "slow-release acidification-hydrophobic aggregation-enzymatic crosslinking", the gel strength (4.50g / cm 2 ) and water holding capacity (100%), and the synergistic optimization effect of microstructure and molecular force is significant; Example 6 constructs a flexible hydrogen bond network by virtue of its polyhydroxy characteristics, and its elasticity (14.73mm) is outstanding but its strength is limited; Example 7 enhances local cross-linking by calcium chelation, and its water holding rate is close to that of glucono-δ-lactone, but the process cost is relatively high. In comparison, Comparative Example 1 lacks the assistance of organic acid and only relies on the basic activity of TG enzyme, resulting in a loose network and low functional performance. The present invention provides a process option for the precise modification of plant protein gels.

[0190] The content of the present invention is not limited to the implementation methods illustrated in the embodiments. Any routine modifications and equivalent replacements made by ordinary technicians in this field to the technical solutions of the present invention after reading the description of the present invention are within the scope of the specific implementation methods of the present invention.

Claims

1. A method for preparing soy protein isolate gel by using organic acid compound TG enzyme, characterized in that: The following steps are involved: Step 1: prepare a soy protein isolate solution with a mass volume ratio of 12% and stir at room temperature; Step 2, adding 40 U / g TG enzyme to the protein solution to mix the TG enzyme and the protein solution; Step 3, adding an organic acid to the protein solution to which TG enzyme has been added and stirring to obtain a mixed solution, wherein the organic acid is any one of glucono-δ-lactone, lactobionic acid, and maltobionic acid; when the organic acid is glucono-δ-lactone, the mass volume ratio of glucono-δ-lactone to the protein solution is 0.4% to 1.0%; when the organic acid is lactobionic acid, the mass volume ratio of lactobionic acid to the protein solution is 0.8%; when the organic acid is maltobionic acid, the mass volume ratio of maltobionic acid to the protein solution is 0.8% to 1.0%; Step 4: Pour the mixed solution into a container, seal it, and place it in a 40°C water bath for 1 hour; Step 5: Transfer the mixture to a water bath and heat at 95°C for 30 min. Step 6: After heating, remove the sample and cool in an ice water bath for 10 minutes. Step 7: storing at 4° C. overnight to obtain the soy protein isolate gel.

2. The method for preparing soy protein isolate gel using organic acid compound TG enzyme according to claim 1, characterized in that: The soy protein isolate solution in step 1 was stirred at 500 rpm at room temperature for 2 h.

3. The method for preparing soy protein isolate gel using organic acid compound TG enzyme according to claim 1, characterized in that: After adding TG enzyme in step 2, the mixing method is stirring, and the stirring time is 30 min.

4. The method for preparing soy protein isolate gel using organic acid compound TG enzyme according to claim 1, characterized in that: During the reaction in a 40° C. water bath for 1 h in step 4, the solution was stirred at a speed of 500 rpm.

5. The method for preparing soy protein isolate gel using organic acid compound TG enzyme according to claim 1, characterized in that: In step 5, during the heating in a 95°C water bath for 30 min, the power of the heating equipment is 800 W.

6. The method for preparing soy protein isolate gel using organic acid compound TG enzyme according to claim 1, characterized in that: During the ice-water bath cooling in step 6, the mass ratio of ice to water is 1:

2.

7. The method for preparing soy protein isolate gel using organic acid compound TG enzyme according to claim 1, characterized in that: The room temperature is 18-30°C.

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